Every ontological database uses as its foundation Resource Description Framework (RDF), Resource Description Framework Schema (RDFS) and Web Ontology Language (which has come to be known as OWL). RDF is the simple notion that any knowledge can be represented as a tuple or statement containing a subject, predicate, and object. While RDF does not impose any constraints on the values for the subject, predicates, and objects; RDFS adds rules. After RDFS was introduced, it was recognized that there was a need for a ‘rules’ language that allowed patterns of knowledge to be expressed as rules. OWL was developed to allow knowledge to be inferred from an existing set of RDF information, using inferencing rules.